Although the heat pump principle is not new, extensive use of this energy concept in practical devices has only been recently accomplished. Now that energy conservation is of prime importance, greater use of heat pump systems is being made to save energy and achieve lower initial costs of heating and cooling equipment. Heat pumping in its simplest terms is described as pumping heat from a low energy level to a high energy level and using the resulting heat for space and domestic water heating.
Many forms of heat pump systems have been devised. These systems normally include a refrigerant fluid compressor that is interconnected with two heat exchanger units. The two heat exchanger units are alternatively operated as evaporators or condensers depending upon the positioning of a directional control valve in the interconnecting refrigerant fluid conduit for heating or cooling modes of operation. One heat exchanger unit is associated with heating or cooling apparatus, such as a fan and coil type condenser or evaporator. The other heat exchanger unit is operated to either add heat to the system or remove heat by dissipation.
While the heat pump system is inherently an efficient heating and cooling system, there are nevertheless factors which decrease efficient operation of such heat pump systems. One such factor is that where water is used as a heat source in a heat pump system, the water temperature should remain relatively constant to ensure that the heat pump operates close to ideal conditions to maintain a high coefficient of performance. Particularly, in a water source heat pump, fluctuations in the water temperature directly affect the operating efficiency of the system.
A need has thus arisen for a heat pump system having the ability to compensate for changes in water temperature of the water utilized as a heat source in such systems by controlling one, the amount of water flowing through one of the heat exchanger units in the system and second, by controlling the temperature of the water in the preheat exchanger and then through one of the heat exchanger units in the system. A control of such water flow and temperature will enable the heat pump to operate close to ideal conditions during operations.